When the U.S. Justice Department revealed plans to release previously confidential guidance memos addressing the disclosure of U.S. lobbying work for foreign clients, a tiny circle of Washington lawyers last month cheered the move as an overdue step toward transparency.

For years, that niche in the Washington legal circles grumbled about the Justice Department’s practice of concealing advisory opinions on the Foreign Agents Registration Act, or FARA, a 1938 law that in certain instances requires law firms and lobby shops to disclose their advocacy for foreign clients.